Evidence-based medicine shifts the basis for clinical decision making from intuition and unsystematic clinical experience to the examination of evidence resulting from clinical research. Evidence-based medicine is the same as good clinical research. The selection of a proper study design for a specific study objective is the most important cornerstone of good clinical research. Evidence-based medicine places great importance on the design of a study, with optimum evidence being obtained from the randomised, controlled clinical trial. However, various study designs are equally important-if properly used-in the process of searching for solid and important evidence for use in clinical practice. There should be an emphasis on a quality improvement shift in research design from retrospective to prospective, cross-sectional to longitudinal, uncontrolled to controlled, and non-randomised to randomised. The reasons for using suboptimal study designs in clinical research are the lack of formal research training and the pressure to obtain academic output without being motivated. Research design is one of the most important aspects to study and practice, and there are four simple rules: (1) avoid retrospective studies; (2) focus on prospective studies; (3) use controls, randomisation, and blinding; and (4) always discuss the research design with an experienced researcher or statistician before commencing the study.